The proposed series of three studies is designed to investigate the process of word learning in early language development. The focus of most previous research in this area has been on the nature of the child's word meanings. These studies analyze spontaneously produced child speech, using methods borrowed from linguistic semantics. Recently, however, some researchers have been employing experimental techniques, the so-called "lexical training" methods, to study early lexical development. Their focus has not been on the child's word meanings, but rather it has ben on factors, both organismic and environmental, that affect the process of early work learning. They have identified such effective parameters as: the frequency and speacing of adult language models, and the prototypicality of the adult model's referent. The proposed studies are designed to use a lexical training methodology to investigate the cognitive-developmental factors underlying early lexical development. The factors investigated emanate from a three component model of lexical development whose basic premise is that language acquisition is a cognitive-developmental process operating in a social-conventional domain. One experiment is proposed for each component. Experiment 1 is designed to test the effect of a specific cognitive stage change on the child's ability to learn specific types of words. Experiment 2 is designed to investigate the effect on the child's language of attentional parameters: where the adult's attention is focused, where the child's is focused, and whether or not they are in a state of joint attention. Experiment 3 is a pilot study designed to investigate the role of the child's existing semantic capabilities, and the expectations these entail, in learning new words. Because these studies are guided by a coherent theoretical framework, they should provide us with valuable information about the factors affecting early lexical development